Apparatus for providing storage tanks with a gas blanket



March 17, 1970 H. G. EDIGER ETAL APPARATUS FOR PROVIDING STORAGE TANKS WITH A GAS BLANKET Filed June 10. 1968 INVENTOR'.

HEINZ G. EDIGER GEORG MIELKE THEER ATTORNEY United States Patent 3,501,049 APPARATUS FOR PROVIDING STORAGE TANKS WITH A GAS BLANKET Heinz G. Ediger and Georg Mielke, Hamburg, Germany,

assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed June 10, 1968, Ser. No. 735,660 Claims priority, application Germany, June 9, 1967,

D 53,305 Int. Cl. B65d 25/00 US. Cl; 220-85 5 Claims ABSTRACT OF THE DISCLOSURE Apparatus and method for providing a liquid storage tank with a gas blanket comprising a storage tank for storing therein a liquid and a pressurized gas supply means for supplying gas under pressure to the tank. A supply line is coupled to both the tank and the gas supply means. Pressure control valve means is coupled to the supply line and regulated by the pressure within the storage tank. A return line is coupled to both the supply line and the gas supply means. Compressor means is disposed in the return line for compressing the gas therein and second-mentioned pressure control valve means is coupled to both the'compressor means and the return line wherein the pressure in the supply line regulates the pressure of both pressure control valve means. I

' BACKGROUND OF THE, INVENTION Field of the invention The present invention relates to a method and apparatus for providing storage tanks for: liquids, particularly Description of the prior art Storage tanks are normally blanketed with a blanketing gas, usually with a gas which is poor in oxygen, by supplying a gas stream at slightly excess pressure and allowing the excess gas to escape by means of a pressuremaintenance valve. The quantity of the gas supplied must be sufiicient to equalize any sudden variations in pressure and volume within thegas cap in the storage tank, for example when the' tank is being emptied. As a blanketing gas, use is normally made of exhaust gas passed from a suitable furnace through the necessary coolers and condensation traps. These blanketing gas plants are large and expensive to operate and maintain; they are therefore only suitable for relatively large tank installations, for example, in oil refineries. They can be simplified by using steel bottles containing highly compressed nitrogen instead of the complicated combustion and cooling installations. However, the continuous consumption of pressure gas makes plants of this type too expensive for most purposes.

In contrast, for the storage of at least partially highly volatile liquids such as liquefied hydrocarbon gases or crude oil, use is made of apparatuses which prevent gases from escaping from the storage tanks. It is known, for instance, to group storage tanks for liquefied gas, with the use of compressors, in such a way (US. patent specification 2,885,109) that the lack or excess of gas from tanks which are being emptied or filled is equalized over these tanks or over tanks which are not being emptied or filled. It is also known to discharge the excess gas from crude oil tanks through an exhauster into a gathering 3,501,049 Patented Mar. 17, 1970 pipeline, and to make up any deficiency of gas from the same gathering pipeline by means of a bypass line for the exhauster (US. patent specification 2,899,013). Thus these measures, too, maintain a protective blanket in the storage tank. However, a condition of their use is the presence of highly volatile liquids, and they are also by nature only applicable in large tank installations.

It has now been found that certain difficult or nonvolatile mineral oil products, in particular many highmelting bitumens in the hot-liquid state, should be stored under a gas blanket to prevent quality deterioration. In the processing plants, whose farms usually contain only a few tanks, these products have to be maintained at temperatures in excess of 200 C. The conventional blanketing gas plants, however, are not suitable on account of their size, quite apart from the fact that continuous venting of blanketing gas loaded with bitumen vapors would create a very unpleasant smell in the installation and surroundings.

SUMMARY OF THE INVENTION The apparatus and method according to the invention for providing storage tanks with a gas blanket is characterized by a pressure-gas container for the blanketing gas supply, a supply line with a control valve regulated by the pressure in the storage tank, and a return line with a compressor arranged parallel to the control valve and also regulated by the pressure in the storage tank.

The storage tank preferably is sealed off as completely as possible from the ambient atmosphere and is preferably provided with a safety valve against excess pressure and subatmospheric pressure in order to prevent damage in the event of unexpected failures. The conventional diphatch is better avoided, since it allows blanketing gas to escape, at least during gauging. The storage tank is preferably suitably fitted with a closed level gauge (known per se), for example a float device with magnetic indication transfer.

With this apparatus, the supply of blanketing gas shuttles, depending on the operating conditions, between the pressure-gas container and the virtually pressure-free storage tank, and unpleasant vapors are thus prevented from escaping into the atmosphere.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic illustration of a preferred embodiment for carrying out the teachings of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a pressure tank 1, which contains a supply of blanketing gas, is connected by way of supply line portion 9 to a pressure control valve 2. Supply line portion 10 leads from valve 2 to a main supply line 3 leading to a storage tank 4. Control valve 2 is regulated by conventional pressure control means 11, coupled to both valve 2 and supply line 3. Supply line 3 also leads to a return line 21 having a control valve 12 and a compressor 5 which is controlled by a conventional compressor control means 13 coupled to pressure control means 14. Control means 14 is also coupled to supply line 21 which is in turn coupled to supply line 3 so that the pressure in supply line 3 regulates both the pressure of control means 11 and 14 and thus control valve 2 and compressor 5. Return line 21 then passes from compressor 5 through a nonreturn check valve 6 and into pressure tank 1. Supply line 3 is connected to storage tank 4 without shut-off or throttling means and its length and crosssectional diameter is so dimensioned that it maintains the same pressure over substantially its entire length as the pressure in storage tank 4. A conventional devaporizing or ondensing means 7, such as a liquid separator or cooler, v, p

'- disposed between supply line 3 and storage tank 4 for ondensing any gases exiting from tank 4 before any quids from the gases enter line 3. Vacuum safety valves and 15 may be provided at storage tank 4 and pressure lIlkS 1, respectively. The pressure in pressure tank 1 may e controlled by pressure control valve 16. A pressurized as supply means 17, controlled by control valve 18, is referably coupled to supply line 3. Liquids into and out f storage tank 4 may be selectively introduced and ithdrawn by means of control valves 19 and 20, respecvely, as illustrated in the drawing. I

Since, as a rule, the storage tanks in question will stand p better to a slight excess pressure than to sub-atmosheric pressure, the control is suitably set in such a way rat the control valve 2 responds at the latest when the mbient pressure has been reached, while the compressor is switched on at an excess pressure of, for example, a mm. water column. The control range must, of course, e contained within the response limits of the excess pres- JIC and vacuum safety valve 8; in a suitable embodiient, only approximately the middle third of the safety ange is utilized. To begin operations, the entire system is lled up with nitrogen from a suitable gas supply means 7, such as steel bottles, until a pressure of several g./cm, is reached in the pressure tank 1. At a later :age the leakage losses only have to be made up from me to time, when the pressure in this tank has dropped such a level that when the storage tank 4 is being mptied rapidly the pro-vision of a gas blanket by way f the control valve 2 is no longer guaranteed.

EXAMPLE By way of example, it was found that a 45 m. storage ink in which a special bitumen is stored at 200 C.-230 t. and which is filled, when necessary, at a pumping peed of approximately 12 m. /h., canbe maintained :liably under blanketing gas (nitrogen) under all operatig conditions by means of the following equipment: a ressure tank 1 with a capacity of 5 m. and the operating ressure of 8 kg./cm. an electromagnetic control valve ID-lO 2, controlled by a pressure switch at 0.10 mm. ater column; a shuttle lien NW-25 3; a signal-stage :ciprocating compressor 5, with a delivery of 16 m. /h. I: a compression pressure of 8 kg./cm. controlled by a ressure switch at 55-63 mm. water column; and an air ooler 7 from ribbed cooling pipes NW-25 with a total :ngth of approximately 8 mm.

In addition to the foregoing, the apparatus and ethod f this invention appreciably reduces the formation of ake deposits in bitumen storage tanks; consequently the fequency of cutting the tanks down for cleaning is dereased. Thus, the apparatus of this invention is particulrly applicable to the gas blanketing of hard grades of itumen with high storage and processing temperature such as ZOO-260 C.).

We claim as our invention: n H

1. Apparatus for providing a liquid storage tank with a gas blanket comprising:

a storage tank adapted to contain therein a liquid;

- pressurized blanketing gas supply means for supplying a blanketing gas under pressure to said tank;

a supply line coupled to both said tank and said blanketing gas supply means;

pressurized make-up gas supply means coupled to said supply line for selectively admitting gas under pressure thereto;

a valve-in said supply line;

first pressure control meansoperatively coupled to said supply line and regulated by the pressure within said storage tank to control said valve;

a return line coupled to both the supply line and said blanketing gas supply means; I I compressor means disposed in said return line for compressing said gas therein; and w second pressure control means operatively coupled to both said compressor means and said return line whereb the pressure in said supply line regulates the pressure of both said first and second pressure control means. y p

2. The apparatus of claim 1 including de-vaporizing means disposed in said supply line for condensing any gases leaving said storage tank.

3. The apparatus of claim 2 whereby said storage tank is substantially sealed'ofi from the ambient atmosphere; and

safety'valve means associated with said storage tank for selectively protecting said tank from both excess and sub-atmospheric pressures.

4. The apparatus of claim 1 wherein the Supply line has a length and cross-sectional diameter such that said supply line maintains the same pressure over substantially its entirelength as the pressure Within said storage tank.

5. The apparatus of claim 1 whereby said storage tank. is substantially sealed 01f from the ambient atmosphere; and

safety valve means associated with said storage tank for selectively protecting said tank from both excess and sub-atmospheric pressures.

References Cited UNITED STATES PATENTS 1,147,729 7/ 1915 Hurlbrink. 1,172,884 2/ 1916 Gungerich. 2,870,936 1/1959 Clayton. 2,899,013 8/1959 Carter.

' FOREIGN PATENTS 7,709 1907 Great Britain.

JOSEPH R. LECLAIR, Primary Examiner 

